this sounds really similar to how the tool works and processes emails, too.

Would you feel this would be more helpful if the tool just silently manages the emails and does not send any replies to the original sender then?

The paradox is that the person most likely to do extra work is the person you want to hear from least. If someone felt the need to pay (for example) $5,000 to talk to me, it's probably because they don't feel they have a chance of getting my attention otherwise. I'd also never pay someone 5 grand if I'm the one offering them something.

A Captcha isn't 5 grand, but I think the same principle applies. If I'm putting a request for proposal to 10 vendors, I'll probably disqualify the one that makes me verify that I'm a human. It's not like I'm short of qualified companies.

Look, this is HN it's not the typical technical ability or email needs. Just because I wouldn't use this doesn't mean nobody would.

You've made it, try it, maybe people will find enough benefit here to pay you.